Composite stone as doorway threshold

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Customer wants to have hardwood in doorway cut out and a pre-fab composite stone dropped in the void as a threshold/or transition. This goes from a hall into a bathroom with composite tile. The hall is 3/4" oak over shiplap at 45 degree angles. Joists are on 16's. I'd need to cut out the hardwood to one side of the jamb and cut out a bit of tile and plywood on the bathroom side of the casing.
If I removed the hardwood and plywood what would I use as an adhesive to support the Stone? Silicone?
The pre-fab transition has rolled edges, so it looks as it was made for this type of project?
Stone is 3/4 and so is the floor, so it can't be mudded in.

 

[Floorist]

You will figure it out. I don't think there is anything you can't do.

 

[highup]

I can't play Jeopardy, write books or remember where I left my keys. ...that's just the tip of my lack of knowledge iceberg.
That's why I come here. Help from you guys make me look smart to my customers. I don't tell em where I get my smarts from.

 

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Here's the doorway. Arrows show where the wood would need to be cut and where the Alterna vinyl tile would be cut out so the stone could be slid into place becoming almost flush. There are holes in the tile and a dent where the metal trim used to be. There is 3/4 inch plywood under the tile and that would be removed too.
The second image shows where the joists are in the doorway. One joist is at the beginning of that tape measure and the next at 16 inches.

 

[highup]

Dupe

 

[Ernesto]

Glue it in with some moisture cure urethane adhesive. Used all the time for mixed media wood n tile

 

[highup]

Much appreciated.

 

[highup]

Glue it in with some moisture cure urethane adhesive. Used all the time for mixed media wood n tile

I guess the homeowner wants to do this. Gonna start on it tomorrow.
Talked to the guy that does the stonework and he said to use thinset. That would make getting to the exacact height really difficult. I want it to set about 1/8" above the wood on one side and Ceramica tile (VCT tile) in the bathroom.
A polyurethane adhesive would cure hard like the thinset. Those wood adhesives dry flexible don't they?
If I did use a wood floor adhesive, what notch? 1/8 V

 

[highup]

I'm thinking not just cutting the oak to get the correct width. I'm thinking of removing the ship-lap down to the joist also. The ship lap has too much movement. I can tell because they removed the oak flooring in the dining room. You can feel movement walking on the floor there, so no way do I want movement in this doorway.
I'm thinking to not only cut out the ship lap, but cut a notch out of the two joists about 5/8 deep and 5 1/8" wide. (same width as the threshold material) That way the single layer of wobbly ship lap can be replaced with two layers of 3/4" plywood screwed together. It would be a lot stronger. The ship lap is at a 45 degree angle to the joists. Joists are 12 inches, so making a 5/8" deep notch on the top side isn't going to compromise anything.

 

[highup]

Well, it's a done-did moment. I talked to tile guys and Latacrete and nobody jives. The local stone people said use epoxy.
Latacrete said to use 254 Platinum. I said I have access to 253 Gold. He said that will work. CPT One said a particular wood adhesive.
Is there a wrong way to install a threshold? ...seems not.
I could only find a 1/4 by 3/8 trowel. I needed to put a 1/4" bed under the threshold piece to bring it up to the height I needed. I really needed a 1/2 inch by 1/2" trowel by my estimation to achieve my 1/4" depth.
I used the Latacrete 253 because it was available.
I lightly troweled the surface of the plywood with my trowel to about 1/4 inch depth. In theory, I made this trowel notching "larger" by making an approximate bed of mortar 1/4 inch deep, then troweling over it lightly a tad deeper. I also heavily back buttered the threshold piece.
First attempt was too much thinset............it was oozing thinset on both sides of the threshold before the piece was fully set to it's required finished height.
Once complete, I locked in a piece a foam between the tile and stone to maintain the gap.. This will allow for a 1/8" of grouting on the bathroom side on Monday. The foam spacer material I used just locked the piece into place so the thinset can set up.
Is $260 too much? Took a lot of guts just to begin creating the void in which to inset the stone. Hard to dodge the screws and make two parallel edges.
The bathroom tile (fake tile) had screws very near the edge of the plywood. How did I find them so that I would know the limitations of my cut?

You're gonna have to ask Selva about that.
Maybe he can post some "magnet" photos.
That would be a great education to newbies and beginners to this trade......... and DIYers.
Selva showed photos many, many years ago using magnets to locate fasteners (or lack of them) beneath the substrate.
Selva, ...............those images you posted years ago on another website and the and how-to's are literally a Godsend. That information has helped me on many.......... and I do mean many jobs.
Those super-magnet tips you showed made this job possible. Without that knowledge you provided I would never have been able to make a cut on this job to within way less than 1/8 of an inch because the tolerances of this opening were so tight with the threshold width being per-determined. I had to be really really exact. If the screws were split in my cut line I would never have been able to make my cut. The job would quite simply, .....not have happened..
I never thank people enough................... But using magnets like you showed to find fasteners.......... ..............man that was good. Thank you sir!